Field
Embodiments of the disclosure relate generally to aircraft structures and more particularly to embodiments for an inlet skin attachment to a supporting bulkhead having mismatched coefficients of thermal expansion.
Background
Current aircraft structures for nacelle and engine cowlings employ skin elements stiffened with attached structural frames having a desired cross section for necessary support of the skin. Lip skins are critical aerodynamic surfaces and it is generally understood that a long lip skin is advantageous to preclude the necessity for a joint with the outer barrel far forward where disruption of the laminar flow region of the lip skin may occur. In many designs the distance between the forward bulkhead outer attachment and the lip skin to outer barrel attachment is quite long. Aerodynamic heating as well as altitude temperature differentials during flight profiles of an aircraft affects the thermal condition of the lip skin and associated support structure. Design and fastening of circumferential stiffeners around the lip skin must take into account thermal expansion of the lip skin and stiffeners. A primary load is generally created by the radial growth of the round nacelle structure and the related circumferential loads due to the substantially circular cross section and differing coefficient of thermal expansion (CTE) between the lip skin and structural elements. Repetitive thermal cycling during flight operations may result in fatigue loading.
It is therefore desirable to provide structural integration for the lip skin and bulkhead attachment that accommodates CTE mismatch and avoids thermally induced fatigue.